A modified retinoblastoma gene construct utilizes the second start codon of the RB gene and encodes for a 94 KD protein (pRB94. It is a markedly more potent tumor suppressor and cytotoxic agent than the wild-type RB protein and has been effective against all tumor types tested to date irrespective of tissue type, RB or other gene status, except for that of telomerase. A long-term objective of this project is to understand the cellular and molecular pRB94 interactions that cause such potent effects. Preliminary results suggest that a key mechanism of pRB94 specific induced tumor cell death may involve the production of rapid telomere attrition and chromosomal crisis. These results make the mechanism(s) of RB94 cell kill and tumor suppression potentially unique from all other agents or modalities examined to date and has occurred in all telomerase positive tumors or immortalized cells but not in tumor or immortalized cells containing an ALT pathway, i.e. telomerase negative cells. RB94 also has been found not to be cytotoxic or growth inhibitory to normal human cells, including urothelial cells, which are also telomerase negative. One approach will therefore be to determine if interference with the normal telomere complex plays a key role in RB94 produced telomere attrition, with subsequent chromosomal instability and cell death. The role of centrosomes and changes in STK15 kinase activity will also be studied in depth. Techniques will be include the use of microarrays, confocal laser scanning, analysis of chromosomal and telomere status, examination of RB94 specific protein interactions by Western blotting and immunochemical staining as well as immunoprecipitation with sequencing of putative RB94-specific related proteins. Studies will be expanded to examine RB94 cell kill in additional telomerase positive or negative tumor cells and genetically altered, non-tumorigenic immortalized cells. Whether or not these changes are caspase dependent will also be studied. Another specific aim is to optimize intravesical gene therapy and determine the effect of AdRB94 on superficial bladder cancer. An intravesical human bladder cancer model developed by us using GFP expressing cells will be utilized for this purpose. To increase adenovirus-mediated transfer the reagent, Syn3, will be used. Syn3 has been found to markedly increase adenoviralmediated gene transfer without being toxic itself. If these studies are successful, it could have a significant influence in developing a new modality of treatment for recurrent superficial bladder cancer and potentially for other tumor types as well as provide the molecular basis for the unique properties of RB94. [unreadable] [unreadable]